Chamber bushing for stud driver



Aug. 21, 1956 R. T. CATLIN ET AL 2,7

CHAMBER BUSHING FOR STUD DRIVER Filed June 23, 1955 2 Sheets-Sheet l INVENTORS HOBf/FT 7. CA rL/lv ALFRED w. HAMA/V/V ARTHUR J. AAA/0A Aug. 21, 1956 R. T. CATLIN EFAL CHAMBER BUSHING FOR STUD DRIVER 2 Sheets-Sheet 2 Filed June 23, 1955 INVENTORS CA HA AETORNE ALFRED 14/. ARTHUR J AAA/0A United States Patent C) CHAMBER BUSHING FOR STUD DRIVER Robert T. Catlin, Trumbull, Alfred W. Hamann, Easton, and Arthur I. Landa, Huntington, Conn, assignors to Remington Arms Company, Inc., Bridgeport, 'C0nn., a corporation of Delaware Application June 23, 1955, Serial No. 517,524

Claims. (Cl. 144.5)

This invention relates to cartridge-powered tools and has particular reference to chamber bushings or cartridge supports for cartridge-powered industrial tools such as stud drivers.

The prior art, as exemplified by such patents as Davis No. 2,145,714, Temple No. 2,549,993, and Temple N0. 2,533,851, shows several examples of removable chamber bushings. Erickson No. 2,697,830 shows another example wherein a family of chamber bushings having progressively restricted orifices were intended for use as a means for controlling the power applied to a stud driven by gas passing through the orifice. The prior art also, as exemplified by Bergman No. 1,445,126 shows the use of a restricted orifice from a cartridge chamber as a means of controlling the ignition and burning char acteristics of the powder in a system wherein the gases of the burning powder can expand in a comparatively large expansion space between the projectile and the orifice. Variations in expansion chamber space produced by variations in the projectile position are employed in Bergman as a means of controlling the range of the projectile.

We have discovered that in cartridge-powered tools it is necessary to provide within the tool or the cartridge case an expansion chamber of volume greater than that of the original volume of the propellent powder in which the charge may be burned. Otherwise, chamber pressures may rise steeply and erratically and such increases in pressure are not reflected as proportionate increases in the velocity of the driven stud. In fact, if an expansion chamber or free volume space is not provided, or is too limited in volume, it is possible for the pressures to increase with a violence which at least approaches detonation and to completely disrupt the barrel and breech closure of the tool before the stud can be moved appreciably.

If the free volume or expansion chamber space provided is grossly in excess of the minimum required to prevent the development of excessive pressures, the pressure acting on the stud or tool can be gradually reduced and the velocity imparted thereto will show proportionate decreases. This variation in expansion chamber space is sometimes employed as a means of regulating the velocity imparted to a projectile or the tool of a cartridge powered device, as set forth in the Bergman patent above cited. Obviously, with a powder-actuated stud driver it is desirable to utilize the most economical possible cartridge case, and to provide adequate power with such cartridge cases it is frequently required that more powder be used than will normally fit within the cartridge case. In such a situation the powder charge is compressed in the cartt'idge'case to provide what is essentially a single solid but readily breakable powder grain. Such a powder grain completely fills the cartridge case and leaves within the cartridge case itself no free volume or expansion chamber. To produce controllable pressures with this type of cartridge, it is necessary that the combustion or expansion space be provided outside the cartridge case Patented Aug. 21, 1956 proper. Considering a cartridge case completely filled with uncompressed powder as having a loading density of 1, it is apparent that the compression of twice that weight of powder into the same cartridge case will provide a case loading density of 2. We have discovered that the volume of an uncompressed charge of powder bears a fairly direct relationship to the volume in which it commences to burn or the total of cartridge case volume and free volume outside of the cartridge case. This relationship is fairly independent of the actual amount of powder compressed within the cartridge case or the loading density within the case itself. The critical factors may be defined in terms of the over-all loading density or the ratio, expressed in percentage, of the volume of the uncompressed charge to the volume of the space in which it starts to burn, before appreciable movement of projectile or stud has taken place.

If the over-all loading density is too great, excessive pressures will be the result, and if the over-all loading density is too small, the stud will not be projected with maximum velocity. Within a fairly critical range of overall loading density and with the same charges of powder, the velocity of stud projection increases only slightly with increased loading density, but pressure is increased quite sharply for the same increase in loading density.

The over-all loading density can be as high as 100% without the development of seriously high pressures and it may be as low as about 60% without seriously reducing the driving power of the stud. The optimum range of over-all loading density appears to fall within the limits of about to These limits on over-all loading density appear to apply about as well to actual cartridge case loading densities ranging from slightly over 1 to as high as 3.

In none of these cases is the actual amount of free volume provided very great-actually, much less than 0.1 cubic inch for any loading we have used. Even this'sm'all external expansion chamber will, however, tend to produce poor ignition of the charge and other ditficulties in regularity of burning the charge, unless there is provided a restricted orifice communicating between the cartridge chamber and the expansion chamber. The provision of such a restricted orifice insures regularity and uniformity of ignition and also assists in breaking up the compressed pellet of powder grains, thereby promoting more regular and consistent burning of the whole charge.

It is therefore the principal object of our invention to provide a chamber bushing so formed as to utilize the most economical cartridge cases and yet insure the projection of studs at maximum velocity and minimum pressure consistent with that velocity, both pressure and velocity being maintained uniform and stable from shot to shot.

It is a further object to provide a chamber bushing which is adaptable to position cartridges of various calibers in such a manner as to permit the use of one firing mechanism with rimfire cartridges of several calibers. To achieve this objective we position certain chambers eccentrically in the chamber bushing so that a segment of the sensitive rim portion of the cartridge occupies the same position as a segment of the rim of another concentrically or eccentrically disposed cartridge case of different diameter formed in a similar chamber bushing. The exact nature of the invention as well as other objects and advantages thereof will become more apparent from consideration of the following specification, referring to the attached drawings in which:

Fig. l is a longitudinal sectional View through a stud driver mechanism, including a barrel having a chamber bushing corresponding to our invention.

Fig. 2 is a vew similar to said Fig. 1, showing a chamber bushing-adapted to take a larger caliber cartridge.

Fig. 3 is a cross-sectional view of the line 3-3 of Fig. 1, showing an end elevational view of the chamber bushing illustrated in Fig. 1.

Fig. 4 is a view similar to Fig. 3 and shows an end .elevational view of the chamber bushing illustrated in Fig. 2. In Fig. 4 the dot-dash circle superimposed on the chamber bushing indicates the relative placement of the head of the small cartridge supported in the chamber bushing of Figs. 1 and 3, and the small dotted circle inside the dot-dash circle indicates the point of the impact of the firing pin on either size of cartridge case.

Referring to the drawings by characters of reference, it will be seen that we have illustrated a fragment of a stud driver comprising a barrel 1, threadably secured to a frame plate 2. The frame plate is securely locked by means of a locking sleeve 3 to a breech block 4, which supports firing mechanism including a firing pin 5. Secured between the breech block 4 and the frame plate 2 is a chamber bushing supporting plate 6 which provides a mounting for the chamber bushing proper indicated generally by the reference character 7. The chamber bushing 7 is formed to define a cartridge receiving chamber 8 and an expansion chamber or free volume space 9. Communicating between these two chambers, both of which are wholly within the chamber bushing, is a restricted orifice section 10. The chamber bushing, it will be noted, is mounted in a recess 11 concentric with the bore 12 of the barrel 1. A stud 13 of any convenient type may be received in the bore 12 and there temporarily retained by the engagement of a retaining disk 14, secured on the head of the stud, with the forward end of the recess 11. Obviously, when a cartridge is inserted into the chamber 8 and fired by the operation of the firing pin 5, powder gas generated within the cartridge case will escape through the orifice and, expanding in the chamber 9, will act upon the rear end of the stud 13 through the medium of the retainer disk 14. The further expansion of the propellent gases will drive the stud down the barrel and into the work in the usual fashion. In Fig. 2 the same relationship exists, but the chamber bushing 15 is provided with a larger .cartridge receiving chamber 16 to accept a cartridge of greater power. As in the other case, the powder gases generated within the cartridge escape through an orifice 17 and, expanding in the expansion chamber 18,.acts directly on the retaining disk at the head of the stud positioned in the barrel 1. It will be noted both by reference to Figs. 2 and 4 that the cartridge chamber section 17 in the bushing 15 is eccentric relative to the bore of the barrel to provide for a positioning of the counterbore 19 which receives the rim of the larger diameter cartridge in a position to receive the impact of the firing pin 5 without requiring any other readjustment than the interchange of the chamber bushings. that the larger diameter chamber bushing 15 is provided with an alignment pin 20 which may be received in a slot 21 in the face of the bushing plate 6 to assist in maintaining the eccentrically chambered bushing in the ing 7 illustrated in Fig. 1 provides Within the orifice sec- It will be noted 7 desired orientation for properly positioning the counterbore 19 beneath the point of the firing pin 5. The bushing 15 is retained within the bushing plate 6 by the interengagement of the retaining pin 22 with a counterbore 23 in the shoulder of the bushing 15. By contrast, the bushing 7 shown in Figs. 1 and 3 is concentric with the bore of the barrel and alignment presents no problems hence, the bushing 7 is not provided with an alignment pin and the retaining screw 22 only loosely extends 'into an annular groove 24 to assist in maintaining the bushing secured to the bushing plate 6.

Considering several specific examples, the .22 Long cartridge case may be loaded with 4 /2 grains of Bulls- Eye powder packed into the cartridge case and occupying a volume of .0203 cubic inch. If this same weight of powder was measured at unit density or was not compressed, its volume would be .0325 cubic inch. When so loaded, the cartridge case has a loading density of 1.6

tion 10 and the expansion chamber 9 a free volume of .0151 cubic inch, or a total volume in which the charge may be burned which is the sum of the volumes of the charge chamber and orifice and expansion chamber or .0354 cubic inch. With this total volume and a charge volume, (uncompressed or at unit density), of .0325, it will be seen that the over-all loading density ready for firing is 91.8%. This cartridge functions very efiiciently for driving studs and the maximum pressures recorded in normal use have been about 87,000 pounds per square inch. With this chamber bushing the orifice 10 is restricted to such a degree that its cross-sectional area is approximately 55% of that of the cross-sectional area of the chamber. This latter value is not particularly critical and the orifice area may be substantially increased, as by powder gas erosion in long use, without introducing ignition problems. Limits from about 35% to about are indicated and it is desirable to start near the caliber Long shot cartridge case in which We have loaded 11.0 grains of Infallible or Unique powder into a cubic volume of .033 cubic inch. This same weight of powder, if measured uncompressed or at unit density, would have a volume of .0809 cubic inch, giving, in the cartridge case so loaded, a car-tridge case loading density of 2.45. This charge may be fired in a chamber bushing similar to that shown in Fig. 1, but one which provides in the expansion chamber and orifice a volume of .066 cubic inch, which, in addition to the .033 cubic inch volume of the charge itself, creates a total volume of .099 cubic inch in which .0809 inch of uncompressed powder is to be burned and results in an over-all loading density of pounds per square inch. In this case, as in the specific example above, the orifice is restricted to 55% of the crosssectional area of the chamber itself and the same limits on orifice area are applicable.

In another specific example we have used the .32 Long cartridge case in which we have loaded 11.0 grains of either Infallible or Unique powder into a volume of .055 cubic inch. The volume of this weight of powder, if measured uncompressed or at unit density, would be substantially .0809 cubic inch and this results in a cartridge case loading density of 1.47. When this charge is burned in a chamber bushing such as that shown in Fig. 2, which provides in the expansion chamber and orifice section a volume of .0298 cubic inch in addition to the .055 cubic inch of volume of the cartridge case, We see that .0809 cubic inch of uncompressed powder has a volume of .0848 cubic inch in which to burn, providing an overall loading density of .955 or 95.5%. In a typical stud driving job using a stud of 550 grains weight with this cartridge, maximum pressures of 75,000 p. s. i. have been recorded. Satisfactory control of the ignition and burning of the cartridge in typical stud driving jobs has been achieved in typical stud driving jobs has been achieved when the orifice area is restricted to 46% of the crosssectional area of the cartridge chamber, and the limits on orifice area above noted seem applicable here also.

Although the pressures noted in the specific examples above may seem high for rimfire cartridge cases to sustain, it should be noted that the chamber bushings provide a counterbore which completely encloses the rim or head section of the cartridge case. It should be further noted that in a system of this type, powder gas is free to enter the section between the forward end of the chamber bushing and the forward end of the counterbore formed in the 7 barrel to receive'the chamber bushing. This resultsin a tendency for the chamber bushing to recoil or set back in the counterbore in the barrel under the influence of gas pressure and maintains the chamber bushing and the cartridge case supported therein during the interval when support is needed, in close and intimate contact with the forward face of the breech block 4. As a result, the head of the cartridge case, which is its vulnerable portion, is quite completely surrounded and supported on all sides by the engagement between the chamber bushing and the breech plate 4. We have not encountered cartridge case failures in several of those instances where experimental cartridges produced pressures so greatly in excess of 100,000 pounds per square inch that accurate estimates of pressure could not be made. Although cartridge cases exposed to such grossly excessive pressures are badly and permanently deformed, extraction of the fired cartridge case from the chamber bushing becomes a problem only when chamber pressures are permitted to materially exceed 100,000 p. s. i., which pressure is at or near that at which the velocity gained by added pressure is insignificant by comparison with the problems involved in containing the pressure.

The conditions described in this application are critical only with respect to the limiting conditions imposed by maximum loads requred to deliver maximum stud driving power. When less than maximum stud driving power is desired, several expedients are available such as the use of less than full loads of propellent powder or the variable positioning of studs in the barrel. The construction we have shown permits the use of these maximum loads to deliver maximum power but prevents their misuse under conditions which might result in the development of dangerously high pressures, or possible conditions approaching charge detonation.

Although only a few specific examples have been shown or discussed herein, we do not consider that the scope of our invention is limited by these examples. For an exact definition of the limits placed upon our invention, reference may be made to the appended claims.

We claim:

1. In a stud driving tool having a barrel with a bore extending therethrough in which a stud may be inserted for explosive projection from the muzzle of the barrel by the combustion of a charge of propellent powder compressed in and completely filling a cartridge case, the invention comprising an improved chamber bushing mounted in the breech end of the barrel, said chamber bushing being formed to define within itself a cartridge chamber to receive and support such a cartridge, a free volume gas expansion chamber in direct communication with the breech end of the bore of the barrel, and an orifice section of lesser cross-sectional area than either of said chambers communicating between said gas expansion chamber and the interior of said cartridge chamber to permit explosive gases generated within said cartridge chamber to expand through said orifice into said expansion chamber to act upon a stud positioned in the breech end of said barrel.

2. The chamber bushing defined in claim 1, the combined volume, enclosed within those portions of the chamber bushing defining the cartridge chamber, the gas expansion chamber and the orifice section, being such that between and 100% of said combined volume is equal to the volume of an uncompressed charge of powder of weight equal to that compressed in said cartridge case.

3. The chamber bushing defined in claim 2, said orifice having a cross-sectional area within a range of from about 35% to about of the cross-sectional area of the cartridge chamber.

4. The chamber bushing defined in claim 1, the combined volume, enclosed within those portions of the chamber bushing defining the cartridge chamber, the gas expansion chamber and the orifice section, being such that between and of said combined volume is equal to the volume of an uncompressed charge of powder of weight equal to that compressed in said cartridge case.

5. The chamber bushing defined in claim 4, said orifice having a cross-sectional area within a range of from about 35% to about 75% of the cross-sectional area of the cartridge chamber.

References Cited in the file of this patent UNITED STATES PATENTS 2,549,993 Temple Apr. 24, 1951 2,679,645 Erickson June 1, 1954 FOREIGN PATENTS 714,931 Great Britain Sept. 8, 1954 

